In recent years, a proximity type IC card, hereinafter abbreviatedly called as "the IC card" has being brought into usage, which is capable of confirming and updating data contained therein without manually passing through a card reader at a card gate or the like, whenever it is used. Such card, called as "a radio-frequency tag" is used as a card tag in an application such as coupon tickets for skiing-ground rifts, coupon or commuter tickets for trains or buses, inventory management, and so on.
The IC card of this kind has a structure as shown in FIG. 4, wherein in (a) of FIG. 4 is a perspective view viewed from the above and in (b) of FIG. 4 a perspective view viewed from the side. As shown in the figure, a fixing resin 34 has a thickness of approximately 0.5 to 2.0 mm to incorporate to fix therein a substrate 31 which has semiconductor devices and discrete electronic parts previously mounted thereon and an antenna 32 formed spiral in the form of a coil. The fixing resin 34 has a surface patched with a film 33, which is formed of polyethylene-terephthalate, or PET, or the like to a thickness of approximately 0.1 mm to have a given mark assigned previously. The substrate 31 has a wiring pattern formed beforehand by printing to allow mounting thereon a semiconductor device such as a micro-computer and memories as well as discrete electronic components involving resistors, capacitors, etc. The antenna 32, serving for transmission and reception of an electromagnetic waves, constitutes a tuning circuit in association with a capacitor forming a resonant circuit.
FIG. 5 shows a general example of a communication system utilizing an IC card. The communication system of FIG. 5 comprises an IC card 10a having an independent data and a card-gate apparatus 20a, which apparatus serves to transmit an electromagnetic wave to supply electric power to the IC card 10a, as well as perform transmission and reception of data. The IC card 10a comprises an antenna 22a for receiving an electromagnetic wave, a rectifying circuit 11 with a capacitor 6 to rectify the received electromagnetic wave for creation of electric power, a power source circuit 12 for supplying an internal circuit of the IC card 10a with power source voltage created from the obtained electric power, a wave-detecting circuit 13 for detecting a data component from the received electromagnetic wave, a modulating/demodulating circuit 14 for demodulating the received data and modulating data to be transmitted, an oscillating circuit 1 for generating a clock signal CP to be supplied into internal circuits, a control circuit formed by a micro-computer and memories, not shown, respectively for processing and storing the obtained data.
On the other hand, the card-gate apparatus 20a comprises a modulating circuit 14a for modulating an electric power signal and a data signal to be transmitted to the IC card 10a, an antenna 22f for transmitting electromagnetic waves for carrying them, an antenna 22g for receiving an electromagnetic wave from the IC card 10a, a detecting circuit 13b for detecting a data component of the received electromagnetic wave from the IC card 10a, a demodulating circuit 14d for demodulating the detected data, and a control circuit 15a for processing the demodulated data to permit the card-gate apparatus, not shown, to perform control depending on the result of data processing. The control circuit 15a comprises a semiconductor device such as a micro-computer and memories, whereas the card-gate apparatus is constituted by a gate device for controlling passage, a guiding display, and so on.
Conventionally, there have been oscillator circuits, which are incorporated into the IC card 10a, such as CR oscillator circuits and ring oscillator circuits, which are easy to configure for integration for a semiconductor device without using components such as ceramic-quartz oscillators and inductance elements. These circuits were often used by incorporation within a semiconductor device. There is shown as an example in FIG. 6 a ring oscillating circuit 9 of a CMOS structure having odd numbers of signal inverters 9m, wherein m=1-n: n is a positive odd number, of such as NAND circuits and inverter circuits. These signal inverters have their input and output terminals for connection of tandem in the form of a ring. The signal inverters 9m have delaying capacitors 3m, respectively, connected to output terminals thereof. The inverter 9n is connected for supply a signal to one input terminal of a NAND 9.sub.1 as well as to an input terminal of an inverter 6 whose output terminal is connected to supply a clock signal CP to other circuitry, not shown, where it can be used as a reference clock for a semiconductor device. The other input terminal of the NAND 9.sub.1 is connected to be supplied with a control signal S for enabling control of commencement and halt of oscillation.
In the meanwhile, ring oscillating circuits, CR oscillating circuits, etc. as stated above were used without problem in devices such as toys, where close precision is not necessary for oscillation frequency. However, they were difficult to use as a device for a card-gate system utilizing an IC card of the proximity type, due to reasons as discussed below.
That is, there is a demand for relatively close precision in oscillation characteristics in a card-gate system utilizing a proximity type IC card, due to the necessity of matching in timing of data transmission and reception between an IC card and a card-gate apparatus. However, an IC card has solely a power source where an electromagnetic wave transmitted from a card-gate apparatus, etc. is received and rectified therein to charge electricity on a capacitor, so that the voltage of the power source is apt to vary depending on the distance from the card-gate apparatus or a state of data reception. The variation of power source voltage causes variation in drivability of each signal inverter, so that each capacitor is changed of its charging or discharging current to vary delay time among the signal inverters, thereby resulting in variation in oscillation frequency. The drivability of each signal inverter also is readily varied by change of temperature or variation of device characteristics incurred through fabrication of a semiconductor device. Thus, oscillation frequency is further varied.
In this manner, the oscillation frequency is varied by various factors. As a consequence, the median oscillation frequency was conventionally controlled by altering the size or the number of transistors involved in a signal inverter, or otherwise vary the size of capacitors to alter the capacitance value. These alterations, however, is impractically troublesome because it necessitates a change of masking or the like used during fabrication of a semiconductor device.
As for oscillating circuits built-in semiconductor devices, there were also no techniques to suppress the variation of oscillation frequency, but for limiting such condition as power source voltage and temperature to meet the frequency-precision requirement.
Incidentally, the usage of external component parts such as discrete oscillators is expected to readily improve the frequency precision. However, it is still difficult to adopt, because an IC card as a product has a limitation in its thickness, the external-part mounting makes the substrate area large, the increased number of pins becomes necessary for packaging, the cost is raised by additional expensive cost, including control cost, for external parts.
It is therefore the object of the invention to form within a semiconductor device an oscillation circuit for presenting an oscillation frequency, which is relatively precise over a wide range of power source voltage and temperature and easy to alter, thereby facilitating the provision of a semiconductor device with less external parts used.
The communication system utilizing an IC card will then be explained briefly based on an example of a general use with reference to FIG. 5. A battery as a power source or the like is not incorporated in the IC card 10a. Consequently, an electric power necessitated by the IC card 10a is given by an electromagnetic wave having a frequency ranging from several hundreds of kilo-hertz to several mega-hertz, which wave is received by the antenna 22a of the IC card 10a upon passing by near the card-gate apparatus provided at a skiing-ground rift gate, etc. The received wave is rectified by the rectifying circuit 11, followed by charging on a capacitor or the like for obtaining necessitated electric power. Only while electric power is sufficient, a given level of power-source voltage is generated by the power source circuit 12, which is supplied to the internal circuit of the IC card 10a for reception, processing, and transmission of data.
The above stated communication system enables the content of data to be confirmed through reciprocal communication through electromagnetic waves without contacting between the IC card 10a and the card-gate apparatus 20a. This eliminates the necessity as required in the conventional magnet-type card of such as taking the card out of a pocket and opening a vehicular window for passing the card through a card-gate apparatus whenever-going through a gate, thereby shortening examination time period with relieved congestion at the gate. Owing to such conveniences, the proximity IC card and the communication system are expected to be in wider use in applications, such as confirming fees on expressways, from now on.
In the conventional IC card, however, communication is possible only while electric power can be supplied after being sufficiently stored on a capacitor through rectification of the received electromagnetic wave. Hence, there is present a problem that the rate of communication cannot be increased because of the necessity of frequent repetition of charging electricity each time the stored electric power becomes insufficient. Another problem lies in that the communication distance cannot be taken longer for a shorter charging time period, because the longer the communication distance the longer duration is necessary for charging electricity. Further, there is left other problem that the antenna of the IC card is used common for getting electric power as well as transmitting/receiving data so that the switching-over between the electric-power reception and the data transmission/reception must be performed depending on a situation. To this end, the IC card is complicate in its internal circuit together with a program thereof, thus extending a development term.
Moreover, ring oscillating circuits, CR oscillating circuits, etc. as stated above were used without problem in devices such as toys, where close precision is not necessary for oscillation frequency. However, they were difficult to use as a device for a card-gate system utilizing an IC card of the proximity type, due to reasons as discussed below.
That is, there is a demand for relatively close precision in oscillation characteristics in a card-gate system utilizing a proximity type IC card, due to the necessity of matching in timing of data transmission and reception between an IC card and a card-gate apparatus. However, an IC card has solely a power source where an electromagnetic wave transmitted from a card-gate apparatus, etc. is received and rectified therein to charge electricity on a capacitor, so that the voltage of the power source is apt to vary depending on the distance from the card-gate apparatus or a state of data reception. The variation of power source voltage causes variation in drivability of each signal inverter, so that each capacitor is changed of its charging or discharging current to vary delay time among the signal inverters, thereby resulting in variation in oscillation frequency. The drivability of each signal inverter also is readily varied by change of temperature or variation of device characteristics incurred through fabrication of a semiconductor device. Thus, oscillation frequency is further varied.
In this manner, the oscillation frequency is varied by various factors. As a consequence, the median oscillation frequency was conventionally controlled by altering the size or the number of transistors involved in a signal inverter, or otherwise vary the size of capacitors to alter the capacitance value. These alterations, however, is impractically troublesome because it necessitates a change of masking or the like used during fabrication of a semiconductor device.
As for oscillating circuits built-in semiconductor devices, there were also no techniques to suppress the variation of oscillation frequency, but for limiting such condition as power source voltage and temperature to meet the frequency-precision requirement.
Incidentally, the usage of external component parts such as discrete oscillators is expected to readily improve the frequency precision. However, it is still difficult to adopt, because an IC card as a product has a limitation in its thickness, the external-part mounting makes the substrate area large, the increased number of pins becomes necessary for packaging, the cost is raised by additional expensive cost, including control cost, for external parts.
It is therefore the object to provide an IC card which is easy to develop of a circuit configuration and a program, as well as a communication system having characteristics improved of communication rate, communication distance, etc.
It is another object to form within a semiconductor device an oscillation circuit for presenting an oscillation frequency, which is relatively precise over a wide range of power source voltage and temperature and easy to alter, thereby facilitating the provision of a semiconductor device with less external parts used.